{"name":"x402 Preflight","purpose":"Check one public x402 endpoint's unpaid payment challenge for Base USDC v2 compatibility","paid_endpoint":"/v1/check?url=https%3A%2F%2Fexample.com%2Fapi","price_usdc":"0.05","limits":"HTTPS public host, one read-only GET, no redirects, 8-second timeout","caveat":"Challenge check only; it does not send a payment or certify settlement"}